The present invention relates generally to processes for producing organic acids, such as lactic acid.
Lactic acid has a number of commercial uses, for example in food manufacturing, pharmaceuticals, plastics, textiles, and as a starting material in various chemical processes. In addition, it is used in the manufacture of polylactic acid, a degradable plastic.
Although organic acids can be prepared by chemical synthesis, production by fermentation is generally less expensive. It is well known to produce lactic acid by fermentation using microorganisms such as Lactobacillus delbrueckii. The broth that results from fermentation contains unfermented sugars, carbohydrates, amino acids, proteins, and salts, as well as organic acids, such as lactic acid. Typically, the organic acid is recovered from the fermentation broth and undergoes further purification before it is used. Purified organic acids recovered from fermentation broths can comprise small amounts of impurities, such as strong acids or certain unknown compounds. Some of these impurities can cause an undesirable color or can interfere with downstream processing of the organic acid. For example, lactic acid as it is sold commercially typically comprises small amounts of impurities such as pyruvic acid, acetic acid, and oxalic acid. Even though present in relatively small amounts, such impurities can have negative effects on polymers produced from the lactic acid. For example, when lactic acid is polymerized to produce polylactic acid (PLA), the presence of even small amounts of pyruvic acid can cause the polymer to have an undesirable yellow color. However, it is difficult to further purify lactic acid that contains only a small fraction of pyruvic acid in the first instance.
Thus, there is a need for improved processes for the production and recovery of relatively pure organic acids, particularly lactic acid.